A crosslinkable hydroxyethylcellulose (“HEC”) treatment fluid (for example, a pill) for use in a well penetrating a subterranean formation can utilize internal and external breakers to break the viscosity of the fluid. However, most of the known internal breakers begin to degrade the polymer shortly after adding them to the pill. This reduces the viscosity of the pill and leads to fluid loss earlier than expected. Moreover, a HEC pill can form a filter cake on the formation face. Due to unavailability of a liquid internal breaker for filter cake removal, an external breaker such as hydrochloric acid is normally required for complete clean up of the filter cake.